Better mileage after long drive

[jeepmor]

14 base FR-S, just over 1 year now.
16k miles

Just took it on an 600 mile trip, getting 1mpg or better driving to work now. Just put 1/2 a tank of real petrol, no ethanol, in on the trip. Seems to have made a difference as I'm getting 27.5 driving to and fro work now.

Any insights. Cleaner fuel system from all petrol super? Not sure, no other changes otherwise.

[mav1178]

How is your MPG being measured?

-alex

[Vincenttam]

Best way to measure it is with gas receipt, pencil and paper. The reading on the odometer is off by a little.

[Tromatic]

Mine reports increased mileage after highway travel as well in fifth or sixth. It's an extremely optimistic little indicator, off by as much as five mpg sometimes from the actual result from doing the math.

[jeepmor]

Data is from the car itself via gauges. I do record fill ups via paper log, but didn't check. Just Looking at the car gauge.

I did have that long drive, and put some pure dino fuel in there. That's likely the anomaly. Wondering if injector are that sensitive or of the pure dino petrol cleaned out my system.

[InspGadgt]

It is normal for long drives to increase fuel mileage. Typically on a long drive you stay at a more consistent speed for longer and do less accelerating so your fuel economy is better. It will stay up there for a bit longer when you resume normal driving patterns but will eventually average back out to what you were getting before.

[humfrz]

It might be within experimental error ........


humfrz

[extrashaky]

Originally Posted by jeepmor

Data is from the car itself via gauges. I do record fill ups via paper log, but didn't check. Just Looking at the car gauge.

Unfortunately you can't trust that thing. It is estimating your mileage by average fuel flow rather than actual miles driven divided by actual fuel used. I installed a mileage calculator on my phone (which does the pencil and paper calculation for you at each fill up), and the car's computer is consistently 3 to 4 mpg off.

If you use the car's computer, that bump after highway use could just be a side effect of the way the car calculates fuel economy. If it's averaging fuel flow, and you just had a long period of lower fuel flow, it's going to average that into the initial calculation back in city driving. It would appear to have a bump whether there really is one or not.

Do it with real numbers instead. There's no reason to have to keep a notebook and do math when you can download an app for your phone that will do it all for you.

[strat61caster]

Nah, assuming the car is in working order with no anomalies the driving cycle, that is the type of driving dictates the fuel economy you get in the moment with no lasting effects.

Highway efficiency > stop and go/city efficiency > wide open throttle

At least, when it comes to your wallet (as pure physics/engineering efficiency favors WOT) combustion engines like steady state.

You're telling us that you're seeing +1 mpg. Is that on your average that you have never reset over 14k miles? Is that on this tank of fuel? Is this on the tank of fuel afterwards? Is this the average of three tanks of fuel?

That statement is open to interpretation so you'll get lots of diagnoses (doctor my stomach hurts, it's either the leftovers or cancer).

By the next tank of fuel you'll be back to normal.

http://www.ft86club.com/forums/showt...18#post2071818

[Zhangy]

Just reset the Overall MPG reading so you get a more accurate picture for your current trip's MPG. Since it showed the long term average, it's not going to change much in just a trip unless of course you reset it

[Tromatic]

Originally Posted by jeepmor

Data is from the car itself via gauges. I do record fill ups via paper log, but didn't check. Just Looking at the car gauge.

I did have that long drive, and put some pure dino fuel in there. That's likely the anomaly. Wondering if injector are that sensitive or of the pure dino petrol cleaned out my system.

E85 is a much better solvent that pure gas is.

[billwot]

Originally Posted by extrashaky

... actual miles driven divided by actual fuel used.

[jblmr2]

It's always been my understanding that non-ethanol gas will produce better mpg than ethanol "enhanced" fuel. Back in the day when all gas was gas, not a gas ethanol mix, I got 2 to 4 more mpg. Around here non-ethanol is hard to find and usually goes for a premium price. You have to do some number grinding to determine if its worth while.

[strat61caster]

Originally Posted by jblmr2

It's always been my understanding that non-ethanol gas will produce better mpg than ethanol "enhanced" fuel. Back in the day when all gas was gas, not a gas ethanol mix, I got 2 to 4 more mpg. Around here non-ethanol is hard to find and usually goes for a premium price. You have to do some number grinding to determine if its worth while.

Yes, ethanol has less energy per unit of volume than 'straight gas' so you will see a mileage decrease as you need to put your foot down a little more to go the same speed. It also corrodes certain rubbers used in older cars and soaks up water which could be bad but typically neither is a problem as most people drive newer cars and we typically burn enough fuel all the time for the moisture collection to ever come to anything meaningful.

Ethanol is more knock resistant so you can run more advanced timing and higher compression ratios to compensate for the lack of energy per volume, that's why E85 tunes show such good gains on stock everything else (Sprint/Outlaw racecars run straight ethanol). And since it is renewable it is likely that ethanol in some form is here to stay to subsidize fossil fuels, it's only cheap now because of government subsidies but the fact that we can grow it and process it on this continent are not something to laugh at.